by Chris Williams

I can only comment on half of the process - the half that consists of making the former over which the canopy will be pulled - because I have always sent my stuff away for the tricky bit.

The principle is simple enough; you make up a solid object, the former, which is in the shape of the proposed canopy.What you make it out of, is really immaterial, and depends entirely on personal preference, and what tools you have available. You can, for instance, make it out of balsa which is physically easy to carve and sand - but can be a bit expensive in the larger sizes. I have made one in the past out of a large block of pine, attacking the shaping process with a variety of power tools until the thing submitted. This time, the finished result is rather heavy and the cost is reflected in the fee required by the Post Office to send it away and bring it back. There are two further considerations:

1. The surface finish: Obviously when the acetate is heated up and pulled over your work of art, any imperfections in the surface are liable to show up on the finished canopy.This means that you have to spend some time on surface preparation.Also to be considered is the effect of the heating process on the surface of the former - as balsa, for instance, is sometimes prone to bubbling under these circumstances. Probably the safest way to achieve the desired result is to glass-cloth the surface, rub it down carefully and prime and sand it down to 600 grit for the best results.
   
   
2. Make it oversize: It wouldn't be much good making the former the same size as the cockpit aperture, as then there would be no space to cut away the excess - and still have enough canopy to fit! The first stage is to fill the aperture with your material of choice and then carve and sand it to the correct shape and profile. Removing it from the fuselage you can now add an inch or so around the base and the back to give you room to manoeuvre

One thing that I have heard of, but not tried myself, is to make up a rough former, pull a final canopy from it, fill it with something like Plaster of Paris, sand this down to a smooth finish and then from this pull your canopy.This is, I believe, what they do at the Vac-forming works with formers of poor quality, but of course it all adds to the cost. Who do I use! Well, I'm sure they wouldn't mind me mentioning their name: Contact:

ROLY HAMBLIN,
SARlK VACFORM,
UNIT 5-6 SlMPLEX lNDUSTRlAL ESTATE,
HlGH ST,
OLDLAND
BRISTOL. BS 15 6TA

Telephone: 0117 - 932 6537